ENGINE COOLING SYSTEM

1999 GMC Suburban

1999 GMC Suburban V8 Four Wheel Drive Automatic 120, 00 miles

I have a problem with my radiator/cooling system. I have done this procedure three times. Drain radiator, put cleaner solution & clean water in radiator, and run for 15-30 minutes per instructio9ns. Then drained, refilled system with fresh water, & run again for 15-30 minutes, drained. Then set up system to back flush, and performed this procedure for a minimum 30 minutes while thermostat open & closed, while draining fluid into a 30 gl can until clear. Then filled system with anti-freeze & water to specified levels. MY PROBLEM IS THAT I HAVE PERFORMED THIS PROCEDURE 3 TIMES WITHIN A 72 HOUR PERIOD, WHILE PUTTING A MINIMAL AMOUNT OF TIME RUNNING ( 2 HOURS) ENGINE. I STILL GET A CHALKY GRAVY COLORED FLUID IN THE RADIATOR. THIS IS A GM VEHICLE THAT HAD THE DEX-COTE TABLET PUT IN AT ASSEMBLY THAT WAS SUPPOSED TO LAST 150,000 MILES. IT SEEMS TO ME THAT, I9S IT POSSIBLE FOR SOME TYPE OF OIL TO BE LEAKING INTO THE RADIATOR? I DO NOT WANT TO DRIVE VEHICLE UNTIL I KNOW THE SOURCE OF THIS PROBLEM. I AM TOTALLY STUMPED. THE VEHICLE DOES NOT SEEM TO BE RUNNING HOT, THERE SEEMS TO BE A VERY SMALL LEAK SOMEWHERE AS I HAVE HAD TO PUT IN A CUP OR TWO OF ANTI-FREEZE. I ALSO FILLED UP THE OVERFLOW TANK TO PROPER LEVEL, & IT APPEARS THAT THIS SAME OIL GLOBULATED MIXTURE IS IN THE OVERFLOW TANK NOW ALSO. WHAT AM I MISSING?

As this is a suburban, you din't mention what V-8 is in it. It cold be a small block or big block. The big block if it has the small 8 mm bolts on the intake had a h abit of loosening up so that could be putting oil in the radiator. Or you could have a head gasket leak or it could be transmission fluid leaking in the radiator from the trans cooling lines. If you don't get the stuff out of the coolant tank everytime your truck cools it will suck that stuff back inside the radiator. The best way to do this is to take the lower radiator hose off the rad and let the water out that way. Then use a cleaner like prestone cleaner not flush. You will hve to run that about 100 miles with just water, nothing else or whatever the instructions say. If you take the coolant tank off clean it with a power washer if you have it. If not then try something like super clean with a strong mix to water. If you can't find it take it to a pro and let him put a pressure tester on it to see if he can find the problem.